KR20210059232A - Non-aqueous electrolyte and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to a non-aqueous electrolyte and a lithium secondary battery including the same, wherein the non-aqueous electrolyte includes: an organic solvent; lithium salt; a nitrile-based compound; and a compound represented by chemical formula 1, and the sum of the content of the nitrile compound and the compound represented by chemical formula 1 is 5 to 8% by weight. In chemical formula 1, R is hydrogen or an alkyl group having 1 to 10 carbon atoms.

Description

Non-aqueous electrolyte and lithium secondary battery including the same {NON-AQUEOUS ELECTROLYTE AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME}

The present invention relates to a non-aqueous electrolyte solution and a lithium secondary battery including the same, and more particularly, to a non-aqueous electrolyte solution having excellent electrochemical properties even under high temperature and high voltage conditions, and a lithium secondary battery including the same.

In general, lithium secondary batteries form an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and a negative electrode including a negative electrode active material capable of storing lithium ions, and the electrode After inserting the assembly into the battery case, it is manufactured by injecting a non-aqueous electrolyte serving as a medium for transferring lithium ions and then sealing it.

Lithium secondary batteries are being applied in various fields such as mobile devices, electronic products, and electric vehicles because they can be miniaturized and have high energy density and voltage. As the application fields of lithium secondary batteries are diversified, the required physical property conditions are gradually increasing. In particular, development of a lithium secondary battery that can be stably driven even under high voltage and high temperature conditions and has a long lifespan is required.

On the other hand, when a high voltage and / or the secondary battery under high temperatures is driven, PF ₆ resulting from lithium salts such as LiPF ₆ contained in the ^{electrolyte-thermally} decomposed to generate the anion for a Lewis acid such as PF _5. Lewis acids such as PF ₅ not only cause decomposition of organic solvents, but also cause side reactions between the electrode surface and the non-aqueous electrolyte by destroying the passivation film formed on the electrode surface, resulting in lower lifespan characteristics due to elution of transition metals and swelling due to gas generation. It causes problems such as phenomenon.

Therefore, development of a secondary battery having excellent life characteristics and swelling characteristics under high temperature and high voltage conditions is required even under high temperature and high voltage conditions.

An object of the present invention is to solve the above problems, and to provide a non-aqueous electrolyte and a lithium secondary battery including the same, developed to realize excellent physical properties even under high temperature and high voltage conditions.

According to one embodiment, the present invention, an organic solvent; Lithium salt; Nitrile compounds; And a compound represented by the following [Chemical Formula 1], wherein the sum of the content of the nitrile-based compound and the compound represented by [Chemical Formula 1] is 5 to 8% by weight.

[Formula 1]

In Formula 1, R is hydrogen or an alkyl group having 1 to 10 carbon atoms.

According to another embodiment, the present invention, the anode; cathode; A separator interposed between the anode and the cathode; And it provides a lithium secondary battery comprising the non-aqueous electrolyte solution of the present invention.

The non-aqueous electrolyte of the present invention contains a nitrile-based compound and a propanesultone compound containing an ester group in a specific amount, so that gas generation and capacity reduction can be effectively suppressed even under high temperature and/or high voltage conditions. Therefore, when the non-aqueous electrolyte of the present invention is applied, a high-voltage lithium secondary battery having excellent high-temperature storage performance can be implemented.

Hereinafter, the present invention will be described in more detail.

Non-aqueous electrolyte

The non-aqueous electrolyte according to the present invention includes (1) an organic solvent, (2) a lithium salt, (3) a nitrile-based compound, and (4) a compound represented by the following [Chemical Formula 1], and the nitrile-based compound and [Chemical Formula 1] It is characterized in that the sum of the content of the compound represented by] is 5 to 8% by weight.

[Formula 1]

In Formula 1, R is hydrogen or an alkyl group having 1 to 10 carbon atoms.

According to the research of the present inventors, it was found that when a nitrile-based compound and a compound represented by Formula 1 are added to a non-aqueous electrolyte to satisfy the above content range, capacity degradation and swelling can be effectively suppressed after high-temperature storage.

This is presumed to be because a product generated by oxidation of the nitrile compound and the compound of Formula 1 during activation and initial charge/discharge processes forms a passivation film on the surface of the anode to prevent side reactions between the anode and the electrolyte. In addition, the nitrile-based compound and the compound of Formula 1 form a complex with the transition metal when the transition metal elution occurs due to repeated charge/discharge and/or high temperature exposure, thereby reducing the lifespan characteristics of the battery and suppressing gas generation. However, when the sum of the content of the nitrile compound and the compound of Formula 1 is less than 5% by weight, the passivation film is not sufficiently formed to obtain the above effect, and when it exceeds 8% by weight, the ionic conductivity of the electrolyte decreases. And, there is a problem that the initial resistance and irreversible capacity increase remarkably due to an increase in viscosity.

Hereinafter, each component of the non-aqueous electrolyte solution of the present invention will be described in more detail.

(1) organic solvent

In the present invention, the organic solvent may include a cyclic carbonate-based solvent, a linear carbonate-based solvent, a linear ester-based solvent, or a mixture thereof. For example, the organic solvent may be a mixture of a cyclic carbonate-based solvent and a linear carbonate-based solvent, or a mixture of a cyclic carbonate-based solvent and a linear ester-based solvent.

The cyclic carbonate-based solvent is an organic solvent having a high viscosity and is an organic solvent capable of dissociating lithium salts in an electrolyte solution well due to a high dielectric constant. For example, ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene It may be at least one selected from the group consisting of carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. Specifically, the cyclic carbonate solvent may be ethylene carbonate, propylene carbonate, and mixtures thereof, and more specifically, may be a mixture of ethylene carbonate and propylene carbonate.

The linear carbonate-based solvent is an organic solvent having a low viscosity and a low dielectric constant, for example, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC ), it may be at least one selected from the group consisting of methylpropyl carbonate and ethylpropyl carbonate. Specifically, the linear carbonate-based solvent may be diethyl carbonate.

The linear ester solvent may be, for example, at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate. . Specifically, the linear ester solvent may be ethyl propionate, propyl propionate, and mixtures thereof, and more specifically, may be a mixture of ethyl propionate and propyl propionate.

Preferably, the organic solvent may include a cyclic carbonate-based solvent and a linear ester-based solvent. When a combination of a cyclic carbonate and a linear ester solvent is used as the organic solvent, not only the long-term cycle characteristics are further improved, but also decomposition of the organic solvent is suppressed during high voltage driving, thereby improving the swelling characteristics.

In this case, the cyclic carbonate-based solvent may be included in an amount of 20 to 60% by weight, preferably 25 to 50% by weight, and more preferably 25 to 40% by weight based on the total weight of the organic solvent. In addition, the linear ester solvent may be included in an amount of 40 to 80% by weight, preferably 50 to 75% by weight, more preferably 60 to 75% by weight, based on the total weight of the organic solvent. When the content of the cyclic carbonate-based solvent and the linear ester-based solvent satisfies the above range, the effect of improving long-term cycle characteristics and high-voltage swelling characteristics is more excellent.

More specifically, in the present invention, the organic solvent may include ethylene carbonate, propylene carbonate, ethyl propionate, and propyl propionate.

In this case, the ethylene carbonate may be included in an amount of 10 to 35% by weight, preferably 15 to 30% by weight, more preferably 15 to 25% by weight, based on the total weight of the organic solvent.

The propylene carbonate may be included in an amount of 5 to 25% by weight, preferably 5 to 20% by weight, more preferably 5 to 15% by weight, based on the total weight of the organic solvent.

The ethyl propionate may be included in an amount of 10 to 30% by weight, preferably 15 to 30% by weight, more preferably 20 to 30% by weight, based on the total weight of the organic solvent.

The propyl propionate may be included in an amount of 30 to 70% by weight, preferably 30 to 65% by weight, more preferably 35 to 55% by weight, based on the total weight of the organic solvent.

(2) Lithium salt

As the lithium salt used in the present invention, various lithium salts in which an electrolyte solution for a lithium secondary battery is commonly used may be used without limitation. For example, the lithium salt, as including Li ⁺ as the cation, and the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 - _{^{, AlO 4 -, AlCl 4 -}} , PF 6 -, SbF 6 -, AsF 6 -, B 10 Cl 10 -, BF 2 C 2 O 4 -, BC 4 O 8 -, PF 4 C 2 O 4 -, PF ^{_{2 C 4 O 8 -, (}} CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, _{^{CF 3 SO 3 -, C 4}} F 9 SO 3 -, CF 3 CF 2 SO 3 -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH _{^{-, CH 3 SO 3 -,}} CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N - , selected from the group consisting of It may include at least any one.

Specifically, the lithium salt is LiCl, LiBr, LiI, LiBF ₄ , LiClO ₄ , LiAlO ₄ , LiAlCl ₄ , LiPF ₆ , LiSbF ₆ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , LiBOB (LiB(C ₂ O ₄ ) ₂ ) At least selected from the group consisting of, LiCF ₃ SO ₃ , LiFSI (LiN(SO ₂ F) ₂ ), LiCH ₃ SO ₃ , LiCF ₃ CO ₂ , LiCH ₃ CO ₂ and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) ₂ Specifically, the lithium salt is LiBF ₄ , LiClO ₄ , LiPF ₆ , LiBOB (LiB(C ₂ O ₄ ) ₂ ), LiCF ₃ SO ₃ , LiTFSI (LiN(SO ₂ CF ₃ ) ₂ ) , LiFSI ((LiN(SO ₂ F) ₂ ) and LiBETI (LiN(SO ₂ CF ₂ CF ₃ ) _{2 A single} substance or a mixture of two or more may be included.

The lithium salt may be included in the electrolyte at a concentration of 0.8 M to 4 M, preferably 0.8 M to 2 M, more preferably 0.8 M to 1.6 M. When the concentration of the lithium salt satisfies the above range, a lithium ion yield (Li+ transference number) and a degree of dissociation of lithium ions are improved, thereby improving output characteristics of a battery.

(3) Nitrile system compound

The non-aqueous electrolyte solution of the present invention contains a nitrile compound.

Nitrile-based compounds are oxidized in the activation process and initial charge/discharge process to form a passivation film on the surface of the anode, and by forming a complex with the transition metal when the transition metal is eluted, side reactions between the anode and the electrolyte are prevented, and the lifespan is deteriorated due to the elution of the transition metal. And gas generation can be suppressed.

The nitrile compound is, for example, succinonitrile, hexanetricarbonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, Cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylaceto It may be one or more selected from the group consisting of nitriles. Preferably, the nitrile-based compound may be succinonitrile, hexanetricarbonitrile, or a combination thereof.

The content of the nitrile-based compound may be 1 to 7% by weight, preferably 1 to 6% by weight, and more preferably 3 to 5% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the nitrile-based compound satisfies the above range, a dense positive electrode passivation film can be formed, and deterioration of battery performance due to elution of transition metals can be effectively prevented.

Meanwhile, when two or more types of nitrile-based compounds are used, the content of the nitrile-based compound means the sum of the contents of the nitrile-based compounds used.

(4) compound of formula 1

The non-aqueous electrolyte solution of the present invention includes a compound represented by the following formula (1).

[Formula 1]

In Formula 1, R is hydrogen or an alkyl group having 1 to 10 carbon atoms, and preferably may be an alkyl group having 1 to 4 carbon atoms.

Preferably, the compound represented by Formula 1 may be 2-acetoxy-1,3-propanesultone.

The oxidation product of the compound represented by Formula 1 forms a passivation film on the surface of the anode, thereby suppressing the occurrence of collapse of the anode structure due to a side reaction between the anode and the electrolyte. In addition, the compound represented by Formula 1 contains a sultone group having high reducibility and is decomposed by a reduction reaction to form an excellent passivation film on the surface of the negative electrode, and to minimize gas generation by suppressing unnecessary reduction reactions of other additives in the electrolyte. do.

The compound represented by [Chemical Formula 1] may be included in an amount of 1 to 7% by weight, preferably 1 to 6% by weight, and more preferably 3 to 5% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the compound represented by [Formula 1] satisfies the above range, a dense passivation layer may be formed on the surfaces of the anode and the cathode.

(5) additive

On the other hand, the non-aqueous electrolyte according to the present invention is not essential, but may further include additives in order to further improve the physical properties of the secondary battery.

For example, the non-aqueous electrolyte of the present invention is 1,3-propane sultone, halogen-substituted carbonate-based compounds, cyclic carbonate-based compounds, borate-based compounds, sulfate-based compounds, phosphate-based compounds, benzene-based compounds, amine-based compounds, and silanes. It may further include one or more additives selected from the group consisting of-based compounds and lithium salt-based compounds.

The halogen-substituted carbonate-based compound may be, for example, fluoroethylene carbonate (FEC)).

The cyclic carbonate-based compound may be, for example, vinylene carbonate (VC) or vinylethylene carbonate (VEC).

The borate-based compound may be, for example, tetraphenylborate, lithium oxalyldifluoroborate (LiODFB), or the like.

The sulfate-based compound may be, for example, ethylene sulfate (Esa), trimethylene sulfate (TMS), or methyl trimethylene sulfate (MTMS).

The phosphate-based compound is, for example, lithium difluoro (bisoxalato) phosphate, lithium difluorophosphate, tetramethyl trimethyl silyl phosphate, trimethyl silyl phosphite, tris(2,2,2-trifluoro It may be one or more compounds selected from the group consisting of ethyl) phosphate and tris (trifluoroethyl) phosphite.

The benzene-based compound may be, for example, fluorobenzene, and the amine-based compound may be triethanolamine or ethylenediamine, and the silane-based compound may be tetravinylsilane or the like.

Meanwhile, the additives may be used alone, or two or more may be mixed and used.

The total amount of the additive may be 1 to 20% by weight, preferably 1 to 15% by weight, based on the total weight of the electrolyte solution. When the additive is included within the above range, a film is stably formed on the electrode, and when overcharged While it is possible to suppress the ignition phenomenon, it is possible to prevent side reactions or additives from remaining or precipitated during the initial activation process of the secondary battery.

Preferably, the non-aqueous electrolyte solution of the present invention may further include one or more selected from the group consisting of 1,3-propanesultone, halogen-substituted carbonate-based compounds, cyclic carbonate-based compounds, and borate-based compounds as additives, More preferably, 1,3-propane sultone, a halogen-substituted carbonate-based compound, a cyclic carbonate-based compound, and a borate-based compound may be further included.

More preferably, the non-aqueous electrolyte solution of the present invention may further include 1,3-propane sultone, vinylethylene carbonate (VEC), fluorine ethylene carbonate (FEC), and lithium oxalyldifluoroborate (LiODFB).

Meanwhile, the 1,3-propane sultone may be included in an amount of 3% by weight or less, preferably 0.1 to 2% by weight, based on the total weight of the non-aqueous electrolyte. Since 1,3-propane sultone is a harmful candidate substance, if it contains more than 3% by weight, stability problems may occur.

The halogen-substituted carbonate-based compound may be included in an amount of 5 to 15% by weight, preferably 5 to 10% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the halogen-substituted carbonate-based compound satisfies the above range, a negative passivation film having excellent conductivity may be formed during initial charging and discharging. If the content of the halogen-substituted carbonate-based compound is too small, the LiF content in the negative electrode passivation film decreases, resulting in a decrease in conductivity, and if the content is too high, a problem of increasing the electrolyte solution viscosity may occur.

The cyclic carbonate-based compound may be included in an amount of 0.1 to 5% by weight, preferably 0.1 to 3% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the cyclic carbonate-based compound satisfies the above range, while minimizing the generation of reducing decomposition gas, the cathode passivation film may be smoothly formed.

The borate-based compound may be included in an amount of 0.1 to 5% by weight, preferably 0.1 to 3% by weight, based on the total weight of the non-aqueous electrolyte. When the content of the borate-based compound satisfies the above range, it is possible to improve the physical properties of the battery while minimizing the increase in the viscosity of the electrolyte and generation of gas.

Lithium secondary battery

Next, a lithium secondary battery according to the present invention will be described.

The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. At this time, the non-aqueous electrolyte is the non-aqueous electrolyte according to the present invention. Since the non-aqueous electrolyte has been described above, a description thereof will be omitted, and other components will be described below.

(1) anode

The positive electrode may include a positive electrode active material layer including a positive electrode active material, and the positive electrode active material layer may further include a conductive material and/or a binder, if necessary.

The positive electrode active material is a compound capable of reversible intercalation and deintercalation of lithium, and specifically, may be a lithium transition metal oxide including lithium and at least one transition metal such as cobalt, manganese, nickel, or aluminum. .

More specifically, the lithium transition metal oxide is a lithium-manganese oxide (eg, LiMnO ₂ , LiMn ₂ O ₄ Etc.), lithium-cobalt-based oxides (e.g., LiCoO ₂ etc.), lithium-nickel-based oxides (e.g., LiNiO ₂ etc.), lithium-nickel-manganese-based oxides (e.g., LiNi _{1 -Y} Mn _{Y O 2 (0 <Y <} 1), LiMn 2 - z Ni z O 4 (0 <z <2), lithium-nickel-cobalt oxide _{(e.g., LiNi 1 -Y1 Co Y1 O 2} (0 <Y1<1), lithium-manganese-cobalt oxide (e.g., LiCo _{1 - Y2} Mn _Y2 O ₂ (0<Y2<1), LiMn _{2 - z1} Co _z1 O ₄ (0<Z1<2), lithium -Nickel-manganese-cobalt oxide (e.g., Li(Ni _p Co _q Mn _r1 )O ₂ (0<p<1, 0<q<1, 0<r1<1, p+q+r1=1 ) Or Li(Ni _p1 Co _q1 Mn _r2 )O ₄ (0<p1<2, 0<q1<2, 0<r2<2, p1+q1+r2=2), or lithium-nickel-cobalt-transition metal (M) oxide (e.g., Li(Ni _p2 Co _q2 Mn _r3 M _S2 )O ₂ (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, p2, q2 , r3 and s2 are the atomic fractions of each independent element, 0<p2<1, 0<q2<1, 0<r3<1, 0<s2<1, p2+q2+r3+s2=1), etc. And any one or two or more of them may be included.

Specifically, the positive active material may be a lithium cobalt-based oxide represented by Formula 2 below.

[Formula 2]

LiCo _{1 - x} M ¹ _x O ₂

In Formula 2, M ¹ is a doping element substituted on a cobalt site, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd , Sm, Ca, Ce, Nb, Mg, B, and may be one or more selected from the group consisting of Mo.

^{Meanwhile, the x denotes the atomic ratio of the doping element M 1} substituted on the cobalt site, and is 0≦x≦0.2, preferably 0≦x≦0.1.

The positive electrode active material may be included in an amount of 80 to 99.9% by weight, preferably 85 to 99% by weight, based on the total weight of the positive electrode active material layer.

Next, the conductive material is used to impart conductivity to the electrode, and can be used without particular limitation as long as it does not cause chemical changes in the secondary battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based substances such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, a conductive polymer such as a polyphenylene derivative may be used, and one of them alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, based on the total weight of the positive electrode active material layer.

Next, the binder serves to improve adhesion between the positive electrode active material particles and adhesion between the positive electrode active material and the current collector. Specific examples of the binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose. Woods (CMC), starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, Styrene butadiene rubber (SBR), fluorine rubber, or various copolymers thereof, and the like, and one of them alone or a mixture of two or more may be used. The binder may be included in an amount of 0.1 to 15% by weight, preferably 0.1 to 10% by weight, based on the total weight of the positive electrode active material layer.

The positive electrode of the present invention as described above may be manufactured according to a method for manufacturing a positive electrode known in the art. For example, the positive electrode is a method of applying a positive electrode slurry prepared by dissolving or dispersing a positive electrode active material, a binder, and/or a conductive material in a solvent on a positive electrode current collector, followed by drying and rolling, or a method of separately applying the positive electrode slurry. After casting on the support of, the film obtained by peeling the support may be prepared through a method of laminating on a positive electrode current collector, or the like.

The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical changes to the battery, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , Silver, or the like may be used. In addition, the positive electrode current collector may generally have a thickness of 3 to 500 μm, and fine unevenness may be formed on the surface of the current collector to increase the adhesion of the positive electrode material. For example, it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The solvent may be a solvent generally used in the art, and dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water And the like, and one of them alone or a mixture of two or more may be used. The amount of the solvent used may be such that the positive electrode mixture can be adjusted to have an appropriate viscosity in consideration of the coating thickness of the positive electrode mixture, production yield, workability, and the like, and is not particularly limited.

(2) cathode

The negative electrode according to the present invention includes a negative active material layer including a negative active material, and the negative active material layer may further include a conductive material and/or a binder, if necessary.

As the negative active material, various negative active materials used in the art, for example, a carbon-based negative active material, a silicon-based negative active material, and a metal alloy may be used.

Examples of the carbon-based negative active material include various carbon-based negative active materials used in the art, for example, graphite-based materials such as natural graphite, artificial graphite, and Kish graphite; Pyrolytic carbon, mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes High-temperature calcined carbon, soft carbon, hard carbon, etc. may be used. The shape of the carbon-based negative active material is not particularly limited, and materials of various shapes such as amorphous, plate, scale, spherical, or fibrous may be used.

The silicon-based negative active material is metal silicon (Si), silicon oxide (SiO _x , where 0<x<2) silicon carbide (SiC), and Si-Y alloy (wherein Y is an alkali metal, alkaline earth metal, group 13 element, 14 It is an element selected from the group consisting of a group element, a transition metal, a rare earth element, and a combination thereof, and may include at least one selected from the group consisting of (not Si). The element Y is Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, It may be selected from the group consisting of Se, Te, Po, and combinations thereof.

The negative active material may be included in an amount of 80% to 99% by weight based on the total weight of the negative active material layer. When the content of the negative active material satisfies the above range, excellent capacity characteristics and electrochemical characteristics may be obtained.

Next, the conductive material is a component for further improving the conductivity of the negative electrode active material, and may be added in an amount of 10% by weight or less, preferably 5% by weight or less based on the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.

The binder is a component that aids in bonding between the conductive material, the active material, and the current collector, and is typically added in an amount of 0.1% to 10% by weight based on the total weight of the negative active material layer. Examples of such a binder include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro. Ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluorine rubber, and various copolymers thereof.

The negative electrode may be manufactured according to a method for manufacturing a negative electrode known in the art. For example, the negative electrode is a method of coating, rolling, and drying a negative electrode slurry prepared by dissolving or dispersing a negative electrode active material and optionally a binder and a conductive material in a solvent on a negative electrode current collector, or the negative electrode slurry on a separate support. After casting to, it can be produced by laminating a film obtained by peeling the support on the negative electrode current collector.

The negative electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface treatment with carbon, nickel, titanium, silver, or the like, aluminum-cadmium alloy, and the like may be used. In addition, the negative electrode current collector may generally have a thickness of 3 μm to 500 μm, and, like the positive electrode current collector, microscopic irregularities may be formed on the surface of the current collector to enhance the bonding strength of the negative electrode active material. For example, it may be used in various forms such as films, sheets, foils, nets, porous bodies, foams, and nonwoven fabrics.

The solvent may be a solvent generally used in the art, and dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone or water And the like, and one of them alone or a mixture of two or more may be used. The amount of the solvent used may be such that the negative electrode slurry has an appropriate viscosity in consideration of the coating thickness, production yield, workability, etc. of the negative electrode mixture, and is not particularly limited.

(3) Separation membrane

The separator is interposed between the negative electrode and the positive electrode, separates the positive electrode and the negative electrode, and provides a path for lithium ions to move, and can be used without particular limitation as long as it is used as a separator in a general lithium secondary battery. On the other hand, it is preferable to have low resistance and excellent electrolyte-moisturizing ability.

Specifically, as a separator, a porous polymer film, for example, a porous polymer film made of polyolefin-based polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer. Alternatively, a stacked structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of a high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, in order to secure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer material may be used, and optionally, a single layer or a multilayer structure may be used.

The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

Accordingly, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

The battery module or battery pack may include a power tool; Electric vehicles including electric vehicles (EV), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEV); Alternatively, it may be used as a power source for any one or more medium and large-sized devices among systems for power storage.

The appearance of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch type, or a coin type.

The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also can be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells.

Example

Hereinafter, the present invention will be described in detail through examples.

Example One

<Preparation of electrolyte solution>

Ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) in an organic solvent mixed in a weight ratio of 20:10:25:45, 1.2M _{LiPF 6} After dissolving so as to be, succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone (NR06) 3% by weight, 1,3-propanesultone A non-aqueous electrolyte was prepared by adding 1% by weight, 0.5% by weight of vinyl ethylene carbonate (VEC), 7% by weight of fluoroethylene carbonate (FEC), and 0.5% by weight of LiODFB (lithium difluoro(oxalato) borate).

<Production of electrode assembly>

A positive electrode mixture was prepared by mixing a positive electrode active material, a conductive material, and a binder in a N-methylpyrrolidone solvent in a weight ratio of 97.59: 1.1: 1.31. _{At this time, LiCoO 2} was used as the positive electrode active material, FX35 (Denka) and CNT (LG Chemical) were mixed in a weight ratio of 0.9:0.2 as a conductive material, and KF9700 (Kureha) and BM were used as a binder. -740H (ZEON) was mixed in a weight ratio of 1.18:0.13 and used. The prepared positive electrode mixture was coated on an aluminum current collector (aluminum) having a thickness of 10 μm, dried at 140° C., and then rolled to prepare a positive electrode.

Next, a negative electrode active material, a binder, and a conductive material are mixed in water at a weight ratio of 95.85:0.5:3.65 to prepare a negative electrode mixture A, and a negative electrode active material, a binder, and a conductive material are mixed at a weight ratio of 97.45:0.5:2.05. A negative electrode mixture B was prepared.

Artificial graphite (Shanshan, G49) was used as the negative active material, and SuperC65 (Imerys) was used as the conductive material.

In addition, in the negative electrode mixture A, BM451B (ZEON) and DAICEL2200 (Daicel) were mixed in a weight ratio of 1.15:2.5 as a binder, and BML302 (ZEON) and DAICEL2200 (Daicel) were used as binders in the negative electrode mixture B It was mixed and used in a weight ratio of 1.15: 0.9.

A negative electrode mixture A and a negative electrode mixture B were sequentially coated on both sides of an 8 μm-thick copper current collector (LS wire), dried at 70° C., and rolled to prepare a negative electrode.

After preparing 7 bicells of anode/separator/cathode/separator/anode structure and 1 monocell of cathode/separator/anode structure by interposing a separator between the anode and cathode prepared as described above, the 7 bicells And one monocell were wound with a long separation film to prepare a stack and folding type electrode assembly.

At this time, as the separator and the separation film, a polyolefin film (ND506B, LG Electronics) coated with BM5 (LG Electronics) was used.

<Manufacture of secondary battery>

The electrode assembly prepared above was accommodated in a pouch-type secondary battery case, and the prepared non-aqueous electrolyte was injected to prepare a lithium secondary battery.

Example 2

Except for the addition of 2% by weight of succinonitrile (SN) and 3% by weight of hexanetricarbonitrile (HTCN), 3% by weight of succinonitrile (SN) and 2% by weight of hexanetricarbonitrile (HTCN) A non-aqueous electrolyte was prepared in the same manner as in Example 1.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 3

Succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone (NR06) 3% by weight instead of succinonitrile (SN) 4% by weight, 2 -A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 4% by weight of acetoxy-1,3-propanesultone (NR06) was added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 4

2% by weight of succinonitrile (SN), 3% by weight of hexanetricarbonitrile (HTCN), 4% by weight of hexanetricarbonitrile (HTCN) instead of 3% by weight of 2-acetoxy-1,3-propanesultone (NR06), A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 4% by weight of 2-acetoxy-1,3-propanesultone (NR06) was added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 5

In the same manner as in Example 1, except that 2% by weight of 2-acetoxy-1,3-propanesultone (NR06) was added instead of 3% by weight of 2-acetoxy-1,3-propanesultone (NR06). A non-aqueous electrolyte solution was prepared.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 6

A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 2% by weight of hexanetricarbonitrile (HTCN) was added instead of 3% by weight of hexanetricarbonitrile (HTCN).

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 7

Hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone (NR06) 3% by weight instead of hexanetricarbonitrile (HTCN) 2% by weight, 2-acetoxy-1,3-propane A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 2% by weight of sultone (NR06) was added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 8

Succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone (NR06) 3% by weight instead of succinonitrile (SN) 1% by weight, hexane A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 2% by weight of tricarbonitrile (HTCN) and 2% by weight of 2-acetoxy-1,3-propanesultone (NR06) were added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Example 9

Ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) in a weight ratio of 20:10:25:45 instead of an organic solvent mixed with ethylene carbonate (EC): Propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) in a weight ratio of 25: 10: 10: 55, except for using an organic solvent mixed in the same method as in Example 1 To prepare a non-aqueous electrolyte solution.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Comparative example One

Ethylene carbonate (EC): propylene carbonate (PC): ethyl propionate (EP): propyl propionate (PP) in a weight ratio of 20:10:25:45 in a non-aqueous organic solvent mixed with 1.2M _{LiPF 6} After dissolving to be, succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 1,3-propanesultone 1% by weight, vinyl ethylene carbonate (VEC) 0.5% by weight, fluoroethylene A non-aqueous electrolyte was prepared by adding 7% by weight of carbonate (FEC) and 0.5% by weight of LiODFB (lithium difluoro (oxalato) borate).

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Comparative example 2

Succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone instead of 3% by weight of 2-acetoxy-1,3-propanesultone (NR06) (NR06) A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 5% by weight was added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Comparative example 3

Succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone (NR06) 3% by weight instead of succinonitrile (SN) 2% by weight, hexane A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 1% by weight of tricarbonitrile (HTCN) and 1% by weight of 2-acetoxy-1,3-propanesultone (NR06) were added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Comparative example 4

2% by weight of succinonitrile (SN), 3% by weight of hexanetricarbonitrile (HTCN), 2% by weight of hexanetricarbonitrile (HTCN) instead of 3% by weight of 2-acetoxy-1,3-propanesultone (NR06), A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 2% by weight of 2-acetoxy-1,3-propanesultone (NR06) was added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Comparative example 5

A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 3% by weight of succinonitrile (SN) was added instead of 2% by weight of succinonitrile (SN).

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Comparative example 6

Succinonitrile (SN) 2% by weight, hexanetricarbonitrile (HTCN) 3% by weight, 2-acetoxy-1,3-propanesultone (NR06) 3% by weight instead of succinonitrile (SN) 4% by weight, hexane A non-aqueous electrolyte was prepared in the same manner as in Example 1, except that 3% by weight of tricarbonitrile (HTCN) and 2% by weight of 2-acetoxy-1,3-propanesultone (NR06) were added.

Then, an electrode assembly and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the non-aqueous electrolyte prepared by the above method was used instead of the non-aqueous electrolyte of Example 1 as the non-aqueous electrolyte.

Experimental example 1: High temperature storage characteristics evaluation

Each of the lithium secondary batteries prepared according to Examples 1 to 9 and Comparative Examples 1 to 6 was charged to SOC 100 under conditions of CC/CV, 0.5C, charging end voltage 4.45V, and 0.05C cut-off, and then at 85°C. Stored at high temperature for 8 hours.

Then, after cooling the lithium secondary battery stored at high temperature, the thickness of the lithium secondary battery was measured, and the rate of increase in thickness compared to the lithium secondary battery before high temperature storage was measured to evaluate the degree of swelling. The evaluation results are shown in Table 2 below.

In addition, charging the lithium secondary battery stored at high temperature under CC/CV, 0.5C, charging end voltage 4.45V, 0.05C cut-off condition, and then discharging it under CC, 0.5C, discharge end voltage 3V conditions in one cycle. Thus, three cycles of charging and discharging were performed, and the discharge capacity after the third cycle was measured. The measured {discharge capacity after the third cycle/initial discharge capacity} × 100 was evaluated as a recovery capacity. The evaluation results are shown in the following [Table 2].

Recovery capacity (%) Swelling (%) Example 1 91.6 6.8 Example 2 91.6 6.9 Example 3 91.2 6.5 Example 4 91.5 6.1 Example 5 92.8 9 Example 6 91.2 8.8 Example 7 90.9 9.3 Example 8 90.8 9.5 Example 9 90.5 8.1 Comparative Example 1 82.9 27.2 Comparative Example 2 89.9 12.6 Comparative Example 3 89.6 10.7 Comparative Example 4 89 10.4 Comparative Example 5 83.8 7 Comparative Example 6 85.9 7.6

As shown in [Table 2], the lithium secondary batteries of Examples 1 to 9 using the non-aqueous electrolyte of the present invention have excellent high-temperature storage performance with a recovery capacity of 90% or more and a swelling degree of less than 10% after high-temperature storage. I did.

In contrast, it can be seen that the lithium secondary batteries of Comparative Examples 1 and 2 using only one of the nitrile-based compound and the compound represented by Formula 1 exhibit lower recovery capacity and higher swelling compared to the lithium secondary batteries of Examples. .

In addition, even if both the nitrile-based compound and the compound represented by Formula 1 are included, when the sum of the contents of these compounds is less than 5% by weight (Comparative Examples 3 and 4), the recovery capacity after high temperature storage is also low, and the swelling is high. Appearance can be confirmed.

On the other hand, when the sum of the content of the nitrile compound and the compound represented by Formula 1 exceeds 8% by weight (Comparative Examples 5 and 6), the swelling characteristics after high temperature storage were relatively good, but the recovery capacity was significantly reduced. Appeared.

Experimental example 2: High voltage characteristic evaluation

Each of the lithium secondary batteries prepared according to Example 1 and Example 9 was subjected to CC at 25°C, 1.3C to 4.1V, 1C to 4.2V, 0.7C to 4.3V, CC/CV, 0.4C As conditions, it was charged to 4.45V 0.05C cut off). Then, it was discharged until it became 3V under CC, 0.5C conditions.

The charging and discharging behavior was set to 1 cycle, and after carrying out such cycles 100 times, the capacity retention rate and the degree of swelling were measured. The measurement results are shown in Table 3 below.

Capacity retention rate (%) Swelling (%) Example 1 98.8 5 Example 9 98.8 6.3

From Table 3, it can be seen that the lithium secondary batteries of Examples 1 and 9 including the non-aqueous electrolyte of the present invention have excellent capacity retention and swelling characteristics even when driving at high voltage.

Claims (14)

Organic solvents; Lithium salt; Nitrile compounds; And it is a non-aqueous electrolyte solution containing a compound represented by the following [Formula 1],
A non-aqueous electrolyte solution in which the sum of the content of the nitrile-based compound and the compound represented by [Chemical Formula 1] is 5 to 8% by weight:
[Formula 1]

In Formula 1, R is hydrogen or an alkyl group having 1 to 10 carbon atoms.
The method of claim 1,
The nitrile compounds include succinonitrile, hexanetricarbonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, In the group consisting of 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile Non-aqueous electrolyte containing at least one selected.
The method of claim 1,
The nitrile-based compound is a non-aqueous electrolyte that is contained in an amount of 1 to 7% by weight based on the total weight of the non-aqueous electrolyte.
The method of claim 1,
R is a non-aqueous electrolyte solution of an alkyl group having 1 to 4 carbon atoms.
The method of claim 1,
The compound represented by [Chemical Formula 1] is a non-aqueous electrolyte solution of 2-acetoxy-1,3-propanesultone.
The method of claim 1,
The compound represented by [Chemical Formula 1] is a non-aqueous electrolyte that is contained in an amount of 1 to 7% by weight based on the total weight of the non-aqueous electrolyte.
The method of claim 1,
The organic solvent is a non-aqueous electrolyte containing a cyclic carbonate-based solvent and a linear ester-based solvent.
The method of claim 7,
The organic solvent is a non-aqueous electrolyte containing 20 to 60% by weight of a cyclic carbonate-based solvent and 40 to 80% by weight of a linear ester-based solvent.
The method of claim 1,
The organic solvent is a non-aqueous electrolyte solution comprising ethylene carbonate, propylene carbonate, ethyl propionate and propyl propionate.
The method of claim 9,
The organic solvent is a non-aqueous electrolyte containing 10 to 35% by weight of the ethylene carbonate, 5 to 25% by weight of the propylene carbonate, 10 to 30% by weight of the ethyl propionate, and 30 to 70% by weight of the propyl propionate .
The method of claim 1,
The non-aqueous electrolyte is 1,3-propane sultone, a halogen-substituted carbonate compound, a cyclic carbonate compound, a borate compound, a sulfate compound, a phosphate group, and a benzene compound, an amine compound, a silane compound, and a lithium salt compound. Non-aqueous electrolyte solution further comprising at least one additive selected from the group consisting of compounds
The method of claim 11,
The 1,3-propane sultone is a non-aqueous electrolyte that is contained in an amount of 3% by weight or less.
The method of claim 11,
The halogen-substituted carbonate-based compound is a non-aqueous electrolyte that is contained in an amount of 5 to 10% by weight.
anode;
cathode;
A separator interposed between the anode and the cathode; And
A lithium secondary battery comprising the non-aqueous electrolyte solution of claim 1.